The present invention relates to a reliable, efficient and economical method and apparatus for the calibration and testing of continuous air monitors (CAMs). More particularly, the invention relates to a dynamic radioactive particle source (DRPS) which is designed to introduce actual radioactivity during real-time testing of a CAM, with a realistic spectra of alpha or beta radiation.
Alarming CAMs are a critical component for worker protection in facilities that handle large amounts of hazardous materials. In nuclear facilities, a CAM sampler alarms when levels of airborne radioactive materials exceed alarm thresholds, thus prompting workers to exit the room to reduce inhalation exposures. To maintain a high level of worker protection, CAMs are required to detect clouds of radioactive aerosols quickly and with good sensitivity.
The monitoring of airborne radioactive contamination is a critical aspect of the control and/or processing of many materials. One of the areas of technology where monitoring the presence of airborne radioactive contamination is of great concern involves the physical handling and disposing of materials classified as radioactive waste. Other areas of concern relate to weapons manufacturing and the processes involving nuclear fission, as the byproducts of these respective activities can be quite hazardous. The safety of workers in these areas and of the public in general is dependent on the ability to quickly detect even trace amounts of hazardous radioactive material released into the environment. When safe levels are exceeded, it is desirable to automatically trigger an alarm so as to warn personnel in the vicinity of the radioactive emission, for in some cases automatic or manual emergency procedures must be implemented to combat the emission.
The accurate triggering of an alarm is critical to safety. CAMs must have adequate sensitivity to alert potentially exposed individuals that their immediate action is necessary. Only two known methods exist for testing and calibrating CAM radiation response functionality. One can use a plated source, which yields a steady-state activity level of simulated collected aerosol. In contrast, the present invention provides a time-varying amount of radiation for testing purposes. Another drawback of the steady state method is the necessity of opening the filter compartment of the CAM in the middle of active air sampling and testing. In some CAMs, this may be a fatal interruption to obtaining a measurement.
Additionally one can test the CAM at an radioactive aerosol test facility, of which there are very few in the world at this time: examples include the Lovelace Respiratory Research Institute in Albuquerque and the EPICEA laboratory (Laboratoire d'Essais Physiques des Instruments de Mesure de la Contamination de l'Eau et de l'Air) in France. The Lovelace Respiratory Research Institute facility includes a station for instrument receipt and inspection, a test bench for determining detection efficiency and energy response for radioisotopes using point-type and area-type electroplated sources and ambient radon progeny; an inline aerosol delivery for testing the internal collection efficiency of sampling heads with fluorescent and other inert aerosols; an aerosol wind tunnel in which inert aerosols can be used to evaluate the inlet and transport efficiency of sampling probes and aerosol collection devices; an epi-fluorescent microscope with automated image analysis and computer-controlled positioning to determine the uniformity of particle deposition on collection filters; and systems for testing the normal response of monitors to ambient radon progeny aerosols or providing aerosols of plutonium or uranium (with or without radon progeny aerosols and interfering dusts) to air monitors under different conditions of concentration and time. The Lovelace air monitor test facility is similar, but not identical, to the EPICEA laboratory. The evaluation of CAMs in the presence of a plutonium aerosol is time intensive, expensive, and requires a specialized facility. Therefore, the present invention provides a DRPS which has numerous advantages to the current methods of CAM evaluation.
Amongst the advantages of the present invention are that it is adaptable for use in a number of different CAMs, it provides non-specialized in-house testing, it has a cost which is approximately 5 times less than the cost of a single test with plutonium test aerosol (for example), it allows for control of CAMs for multiple test scenarios, it is easily repeatable and reusable, it simulates a realistic radioactive aerosol spectrum and it supports iterative development and evaluation of CAMs. By its very nature, the DRPS system also does not foul a tested CAM sampler with radioactive contamination. Additionally, because the present invention does not require difficult and hazardous radioactive aerosol testing, CAM sampler performance could be determined with tests performed on a lab benchtop with no required safety equipment. (In this document, plutonium test aerosol is used as a comparison basis for the use of test aerosol that could be composed of differing radioactive isotopes.)